Air conditioning system with pre-cooler

ABSTRACT

The air conditioning system with pre-cooler includes a compressor; a condenser; an evaporator; a condensate reservoir to collect condensed water discharged from the evaporator; and a condensate pump associated with the condensate reservoir. In one embodiment, the system includes a single pre-cooler that uses condensate to precool air before it reaches the evaporator. In a second embodiment, the system includes a sub-cooler between the condenser and an expansion valve that uses the condensate to pre-cool the refrigerant before it reaches the evaporator. In a third embodiment, the system includes a first pre-cooler that uses condensate to precool air before it reaches the evaporator; a sub-cooler between the condenser and an expansion valve that uses the condensate to pre-cool the refrigerant before it reaches the evaporator; and a second pre-cooler that uses the condensate to pre-cool air before it reaches the condenser.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/012,955, filed Jun. 16, 2014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to air conditioning systems, andparticularly to an air conditioning system that recirculates thecondensate to precool air or to sub-cool refrigerant.

2. Description of the Related Art

An air conditioner (often referred to as “AC”) is an appliance, system,or mechanism designed to extract heat from an area. The cooling is doneusing a simple refrigeration cycle. Its purpose, in a building or anautomobile, is to provide comfort during hot weather. In therefrigeration cycle, a heat pump transfers heat from a lower-temperatureheat source into a higher-temperature heat sink. Heat would naturallyflow in the opposite direction. This is the most common type of airconditioning. This cycle takes advantage of the way phase changes work,where latent heat is released at a constant temperature during aliquid/gas phase change, and where varying the pressure of a puresubstance also varies its condensation/boiling point.

Most high occupancy buildings, such as schools, airports, officebuildings, hotels and shopping malls, have high interior relativehumidity and large amounts of air conditioner condensate. The condensedmoisture can be considered as a byproduct of the air conditioningcooling process. The condensate production depends upon cooling load,humidity, and make-up air volumes. It is claimed that the reuse of thecondensate reduces the need for desalinated water. Collected condensatetemperature is usually between 10° C. and 15.6° C. The cold condensatetypically drips from the evaporator surface into a pan and is dischargedfrom the system through a drain.

One way to increase the efficiency of an AC unit is to lower thetemperature of the air entering the evaporator and compressor units.That is, an air conditioning system can be made more efficient bysub-cooling the liquid refrigerant below the outdoor temperature therebyreducing the amount of flash vapor and allowing a much higher percentageof the refrigerant to be used as effective latent heat. This isbeneficial because it will permit the use of less refrigerant or lowerpressure, each of which will result in a more efficient unit.

Thus, an air conditioning system with pre-cooler solving theaforementioned problems is desired.

SUMMARY OF THE INVENTION

The air conditioning system with pre-cooler includes a compressor; acondenser having a condenser fan associated with the condenser thatforces air to cool the condenser; an evaporator having a fan associatedwith the evaporator that moves cool air out of the air conditioningsystem; a plurality of refrigerant conduits; a condensate reservoir tocollect condensed water discharged from the evaporator; and a condensatepump associated with the condensate reservoir. In one embodiment, thesystem includes a single pre-cooler that uses condensate to precool airbefore it reaches the evaporator. In a second embodiment, the systemincludes a sub-cooler between the condenser and an expansion valve thatuses the condensate to pre-cool the refrigerant before it reaches theevaporator. In a third embodiment, the system includes a firstpre-cooler that uses condensate to precool air before it reaches theevaporator; a sub-cooler between the condenser and an expansion valvethat uses the condensate to pre-cool the refrigerant before it reachesthe evaporator; and a second pre-cooler that uses the condensate topre-cool air before it reaches the condenser.

These and other features of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the basic components of aconventional vapor compression air conditioner (AC) system of the priorart.

FIG. 2 is a pressure-enthalpy (P-h) diagram with additional sub-coolingfrom the sub-cooler arrangement.

FIG. 3 is a schematic diagram of an embodiment of an air conditioningsystem with pre-cooler according to the present invention.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The air conditioning system with pre-cooler utilizes the cold condensatethat typically drips off the evaporator of a conventional airconditioner to pre-cool the incoming air and/or refrigerant in order toachieve greater efficiency. Reducing the air temperature before enteringthe evaporator and the condenser by incorporation of suitablepre-cooling technique and sub-cooling the refrigerant exiting thecondenser will enhance the cooling capacity of the AC system and reducethe power consumption and increase the energy efficiency.

Referring to FIG. 1, a conventional vapor compression air conditioningsystem typically comprises four basic components: the evaporator 102,the compressor 107, the condenser 104, and the expansion valve 103. In atypical refrigeration cycle, the refrigerant fluid flows through thecompressor 107 into the condenser 104, and into the expansion valve 103and finally into the evaporator 102. An internal fan 105 moves theambient air 106 through the condenser 104. Another internal fan 108forces the incoming air 101 through the evaporator 102 and out of the ACunit into the room as cold, air conditioned air 109. When therefrigerant flows through the evaporator 102, moisture is removed fromthe air stream and a cold condensate forms on the surface of theevaporator coil 102. The condensate drips from the evaporator coil 102,which is collected into a condensate tray 110 and is discharged througha drain system. In hot, humid countries like Saudi Arabia, a great dealof condensate is collected from the humid air.

FIG. 2 illustrates the refrigeration cycle of a system of a pressure (P)versus enthalpy (h) diagram with additional sub-cooling that can beattained by adding a sub-cooler between the condenser 104 and theexpansion valve 103 that uses the condensate to pre-cool the refrigerantbefore it reaches the expansion valve 103. The P-h diagram is useful inshowing the amounts of energy transfer as heat and illustrates thethermodynamic characteristics of a typical refrigerant.

In a conventional AC, the refrigerant vapor enters the compressor atstate 1 where it is compressed to higher temperature and pressure. Thehigh pressure super-heated vapor then enters an air cooled condenser atstate 2, where it is cooled by flowing air stream and exits as a liquidat state 3. Then the liquid refrigerant passes through the expansionvalve 103, where it is expanded at constant enthalpy and the pressure issuddenly decreased, the refrigerant becoming a saturated mixture ofliquid and vapor, and finally the mixture enters the evaporator at state4. This cycle can be depicted as 1→2→3→4→1 in FIG. 2. Ambient air ormixed air is forced through the evaporator fan. Because the refrigerantis at a temperature below the dew point temperature of the air stream,it absorbs heat from the air and boils, changing phase from liquid tovapor. The air is now cooled due to heat exchange in the evaporator.During this transfer of energy, only latent heat is absorbed, resultingin the refrigerant remaining at constant temperature.

Additional sub-cooling can be achieved where the cycle commences from1→2→3′→4′→1 as shown in FIG. 2. The process constitutes therefrigeration cycle with a sub-cooler for additional heat rejection atconstant pressure and therefore sub-cooling of the refrigerant enteringthe expansion valve. In a conventional AC system, the cold condensatetypically drips from the evaporator surface into a pan and is dischargedfrom the system through a drain, However, this cold condensate can beutilized to sub-cool the liquid refrigerant exiting the condenser. Theprocess constitutes the refrigeration cycle with a sub-cooler foradditional heat rejection at constant pressure, thereby furthersub-cooling of the refrigerant entering the expansion valve, shownschematically as: 1→2→3′→4′→1.

This sub-cooling can be achieved in different ways. The cold condensatewhich is collected from the cooling coil can be sprayed directly on thesurface of the condenser coil to assist heat rejection from therefrigerant in the condenser and reduce the discharge pressure of therefrigerant. This system may not be that effective, since the heatrejected in the condenser is limited by the temperature of the outdoorambient air. As the size of the condenser coil increases, the amount ofheat rejected in the condenser coil does not increase proportionally.Therefore, the cold condensate has little cooling effect on the largecondenser coils.

Instead of spraying the cold condensate on the refrigerant line exitingthe condenser, it can be sprayed on the sub-cooling portion of thecondenser to further sub-cool the refrigerant. It is also possible tolocate the refrigerant line exiting the condenser coils in thecondensate pan. Thus, the condenser rejects heat to the cold condensatein the condensate pan. However, it is difficult to adopt this type ofsub-cooling technology.

Alternately, the sub-cooling technology with addition of a heatexchanger at the downstream of the condenser to reject heat fromrefrigerant can downsize the compressor and the condenser. In thismethod, the refrigerant flows through a counter-flow condensate heatexchanger positioned between the condenser and the expansion valve andis further sub-cooled by the cold condensate that is collected from thecooling coil. It is a lower temperature heat sink than the outside air.Reducing the air temperature before entering the evaporator and thecondenser by incorporating suitable pre-cooling technique andsub-cooling the refrigerant exiting the condenser will greatly enhancethe cooling capacity of the system and reduce the power consumption.This heat efficiency can be achieved by the newly designed AC with heatexchangers, as shown schematically in FIG. 3.

Referring to FIG. 3, the present air conditioning system includesadditional heat exchangers, which are the sub-cooler and pre-coolers, tofurther lower the temperature of the air as compared to the conventionalAC. In a typical refrigeration cycle, the refrigerant flows through thecompressor 114 into the condenser 109 and into a sub-cooler 107, theninto the expansion valve 106 and finally into the evaporator 115. Thecondensate discharged from the evaporator 115 is collected into acondensate reservoir 104, which is circulated using a condensate pump103 to a first pre-cooler 102 and back into the condensate reservoir104. The condensate is also circulated by the pump 103 to a secondpre-cooler 110 via the control valve 111 and back to the condensatereservoir 104. The cold condensate is also circulated through thesub-cooler 107 located in between the condenser 109 and expansion valve106, thereby further cooling the refrigerant before expansion.

As illustrated in FIG. 3, the ambient air 101 passes through the firstpre-cooler 102, where it is pre-cooled by the circulating condensate.The air then enters the evaporator 115 and it is further cooled anddehumidified. The air temperature drops as it passes through the secondpre-cooler 110 via the pump 103 before entering the condenser 109,thereby providing better cooling of the refrigerant in the condenser109. Also, the condensate is circulated by the pump 103 to thesub-cooler 107 and back to the condensate reservoir 104. The condensatethat is accumulated in the reservoir 104 can be used as water 119 forother purposes.

The heat exchange capacity of a suitable heat exchanger depends on theconfiguration of the heat exchanger, the heat exchange area, the fluidsbeing heat exchanged, the materials of construction of the heatexchanger, and the flow rate of the fluids. The most important elementin maintaining high efficiency is the flow rate of the fluids. Toprovide the highest efficiency, the condensate water must be present andsufficient to extract a reasonable quantity of heat during the limitedperiod of contact. In instances where no condensate water in present, nosub-cooling will take place. Therefore, make up water must beperiodically added in the system. In some conditions, the amount ofcondensate water will be in excess of that required for sub-cooling dueto very high humidity levels, in which case some condensate water can beremoved and used for other purposes.

Sub-cooling decreases the enthalpy of the refrigerant entering thecooling coil, resulting in an increase in the cooling capacity. Theamount of sub-cooling is limited by the temperature of the condensate.An understanding of impacts of equipment, load and climate on the energysavings mechanism is essential to proper application of this technology.The sub-cooling technology requires some custom design and installationfor proper operation and to obtain maximum savings potential. In someembodiments, the condensate is used to improve the performance of theair conditioner by sub-cooling the liquid refrigerant exiting from thecondenser and pre-cooling the incoming air. Therefore, the coolingcapacity of the air conditioner would be enhanced with the reduction ofpower consumption and increases the energy efficiency rating (EER).Thus, the sub-cooler can be used as a retrofit in an existing AC system.

Additionally, the amount of condensate collected from the cooling coilsis estimated based on the thermodynamic analysis for different operatingconditions and compared with the experimental results. After extractingthe heat from the liquid refrigerant, the warm condensate can becollected and re-circulated back to the system after being cooled bymixing it with fresh cold condensate. The excess of the accumulatedcondensate can be used as source of water for non-drinking applicationsas well, such as irrigation, cooling towers make-up water and otheruses. It can be used for drinking purposes after undergoing the requiredmicrobial processes to sanitize the water.

It will be understood that in a first embodiment, the air conditioningsystem of FIG. 3 includes only the first pre-cooler 102, but does notinclude the sub-cooler 107 or the second pre-cooler 110. This system wastested for thirty days in Dhahran, Saudi Arabia. It was found thepre-cooling the air with the condensate before it reaches the evaporatorby 4° C. lowered the air conditioning load by 10%.

It will also be understood that in a second embodiment, the airconditioning system of FIG. 3 includes the sub-cooler 107, but not thefirst pre-cooler 102 or the second pre-cooler 110. In a thirdembodiment, the air conditioning system of FIG. 3 includes the firstpre-cooler 102, the second pre-cooler 110, and the sub-cooler 107.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

1. An air conditioning system, comprising: a compressor; a condenser; anexpansion valve; an air flow conduit having an air inlet and an airoutlet; an evaporator coil disposed in the air flow conduit; refrigerantconduit connecting the compressor, the condenser, the expansion valve,and the evaporator coil; refrigerant flowing through the refrigerantconduit in a continuous cycle from the compressor to the condenser tothe expansion valve to the evaporator coil and back to the compressor; acondensate tank disposed to receive water condensing from air onto theevaporator coil as hot, humid air flows through the air flow conduit; afirst pre-cooler, including: a condensate pump connected to thecondensate tank; a first heat exchanger disposed in the air flow conduitbetween the air inlet and the evaporator coil; and a pre-cooler conduitconnected between the condensate pump and the heat exchanger, wherebycool condensate collected in the condensate tank is circulated throughthe first heat exchanger to pre-cool air before the air reaches theevaporator coil, thereby reducing cooling load on the air conditioningsystem; a sub-cooler disposed between the condenser and the expansionvalve, the sub-cooler having a counter-flow heat exchanger having afirst conduit passing refrigerant flow from the condenser to theexpansion valve and a counter-flow conduit passing condensate collectedfrom the evaporator coil through the condensate pump, the sub-cooler,and back to the condensate tank in a direction opposite the refrigerantin order to cool the refrigerant; and a second pre-cooler disposedadjacent the condenser, the second pre-cooler having a second heatexchanger receiving condensate from the condensate pump and conduitconnecting the condensate pump with the second heat exchanger. 2-3.(canceled)